perf: hoist rest_props exclude list as a module-scope Set#18252
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Rich-Harris merged 5 commits intoMay 29, 2026
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The compiler emitted an inline string array as the second argument to `$.rest_props(...)`. The runtime did a linear `Array.prototype.includes` on this array on every property access via the rest-props Proxy. The exclude list only depends on the component definition, not on the instance, so it can be hoisted to module scope and shared by every instance. Switching it to a `Set` at the same time makes each lookup O(1). For a component like `<Button ...rest />` rendered N times, this turns one per-instance allocation (and N * E linear searches per access, where E is the exclude size) into one module-scope allocation plus O(1) lookups. The legacy `$$restProps` path is unchanged — it mutates the exclude list in its deleteProperty trap, so it can't share a hoisted Set across instances.
🦋 Changeset detectedLatest commit: 23ea587 The changes in this PR will be included in the next version bump. This PR includes changesets to release 1 package
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I'm not completely sure why Tests (24, ubuntu-latest) fails, the other ones are fine 🤔 |
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This PR was opened by the [Changesets release](https://github.com/changesets/action) GitHub action. When you're ready to do a release, you can merge this and the packages will be published to npm automatically. If you're not ready to do a release yet, that's fine, whenever you add more changesets to main, this PR will be updated. # Releases ## svelte@5.56.0 ### Minor Changes - feat: allow declarations in the template ([#18282](#18282)) ### Patch Changes - perf: use `createElement` instead of `createElementNS` for HTML elements ([#18262](#18262)) - perf: store `current_sources` as a `Set` for O(1) membership checks ([#18278](#18278)) - perf: deduplicate identical hoisted templates within a component ([#18320](#18320)) - perf: hoist `rest_props` exclude list as a module-scope `Set` ([#18252](#18252)) Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
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The compiler emitted an inline string array as the second argument to
$.rest_props(...), and the runtime did a linearArray.prototype.includeson it on every property access via the rest-props Proxy.The exclude list only depends on the component definition, not on the instance, so it can be hoisted to module scope and shared by every instance. Switching it to a
Setat the same time makes each lookup O(1).For a component like
<Button ...rest />rendered N times, this turns one per-instance allocation (plus a linear search on every rest-prop access) into one module-scope allocation plus O(1) lookups.The legacy
$$restPropspath is unchanged — it mutates the exclude list in itsdeletePropertytrap, so it can't share a hoisted Set across instances.